Writing variables

To enable the writing of variables, several conditions must be met:

  1. The flag "Enable Write" must be set for the variable. This can be done either during the adding process via the button Add Nodes or afterwards in the parameter settings of the variable.
  2. Before a write command, the "Write Enable" output for the I/O client must be enabled globally. Only then are the write commands generated.
  3. In the "Polling" and "Subscriptions" modes, writing only takes place after a value change within the I/O client. This is particularly important for server restarts. After a server restart, values written once in these modes are not automatically written again, as another OPC UA Client could have written a new value in the meantime and this would then be overwritten by an "old" value.

Setting Enable Write for a variable

In order to add not only an input (Read) element but also an output (Write) element for a variable in the process image, it must be enabled explicitly. This can be done by using the Add Nodes dialog while adding the variables, for example:

Writing variables 1:

Alternatively, this setting can be enabled/disabled at a later stage via the configuration parameters of the variables in the process image.

Writing variables 2:

Enabling write access globally

Before write commands can be sent, they must be enabled globally. This is done by setting the output variable "Write Enable" for the I/O client:

Writing variables 3: